1. Field of the Invention
The present invention relates to a nickel nanoparticle, a method of preparing the same, and a multilayer ceramic capacitor using the same.
2. Description of the Related Art
As electronic parts using a ceramic material, there may be provided a capacitor, an inductor, a piezoelectric element, a varistor, a thermistor, and the like.
Among these, a multilayer ceramic capacitor (MLCC) is a chip type condenser, mounted on circuit boards of a wide range of electronic products to perform important roles of blocking direct current and passing an alternative current therethrough, and being charged with or discharging electricity.
Besides, the multilayer ceramic capacitor is used in functions such as signal bypass, frequency resonance, and the like. The multilayer ceramic capacitor may be advantageous in that it has a small change in dielectric constant according to temperature, has a small size and a high capacitance, and has ease of mountability.
Recently, as an electronic product, such as a computer, a personal digital assistant (PDA), a cellular phone, or the like has been reduced in size, a multilayer ceramic capacitor used in this electronic product is also required to be low in weight, have an ultrasmall size, and have ultrahigh capacitance.
To allow for the ultra small size and ultra high capacitance of the multilayer ceramic capacitor, technologies for ultra thinning and high dispersion of a dielectric layer and an internal electrode constituting the multilayer ceramic capacitor need to take precedence.
In addition, for these technologies for ultra thinning and high dispersion, characteristics of a metal which is a raw material of an internal electrode are important. Hence, it is important to prepare metal nanoparticles having excellent particle size distribution through a Brunauer-Emmett-Teller (BET) method.
Meanwhile, in the related art, a noble metal such as silver, platinum, palladium, or the like, having excellent conductivity, was used as the raw metal, but this metal has recently been replaced by nickel in view of reducing manufacturing costs.
However, since nickel has a lower packing density than a molded body thereof in powder metallurgy, and the shrinkage amount of internal electrodes due to sintering at the time of firing is large as compared with that of dielectric layers, an interlayer short-circuit or disconnection may be easily generated between the internal electrodes.
In order to prevent occurrences thereof, nickel powder needs to have a uniform particle size distribution and excellent dispersibility without agglomerations thereof.
However, the respective nickel nanoparticles may agglomerate during dispersion thereof.
In order to solve this defect, agglomeration between particles due to activation was partially improved by preparing several tens to several hundreds of nanoparticles through a drying or wetting method, forming an artificial oxidation film thereon through a simple heat treatment, and inducing an inactive state therein.
However, this heat treatment may cause a large change in dispersion characteristics due to non-uniform oxidation. Further, after heat treatment, NiO, Ni(OH)2 or CO, and the like, which are inactive, are co-present rather, so that, due to surface non-uniformities thereof, dispersibility may be further deteriorated or agglomeration between particles may be further increased, and thus, there are limits to solving the agglomeration defect of nickel particles.
Particularly, in a Ni—OH structure, difficulties are caused in terms of chemisorption with a dispersant, due to deteriorated acidity of nickel. Here, even when chemisorption with a dispersant occurs, this is highly likely to be dehydration binding of water molecules. If the water molecule is dissociated, the water molecule is adsorbed on polar portions of the resin and the dispersant, so that the function of the dispersant may be deteriorated and the resin may be agglomerated, resulting in deteriorating dispersibility of a paste.
Patent Document 1, the following related art document, does not disclose that 10 to 20 wt % of carboxylic acid is mixed with nickel nanoparticles.    (Patent Document 1) Japanese Patent Laid-Open Publication No. 2006-152439